Whatever their feelings for one another, there were still some obstacles. The King was concerned that his daughter had not had a proper opportunity to meet other eligible young men, and therefore organised parties at Windsor to which suitably classy Guards officers were invited. He was anxious to ensure that she knew she was making the right decision. There was also the question of Philip’s nationality. Some courtiers were concerned that Philip might be compromised by his German relatives.

Princess Elizabeth had no such doubts and in August 1946 Philip was invited to spend part of the summer holiday at Balmoral for grouse shooting and stalking. According to Prince Philip, it was not until then that things became serious. He said: ‘I suppose one thing led to another. I suppose I began to think about it seriously, oh, let me think now, when I got back in forty-six and went to Balmoral. It was probably then that we, that it became, you know, that we began to think about it seriously, and even talk about it.’

At some point during the holiday at Balmoral, Prince Philip proposed to Elizabeth and was accepted. It was to be an unofficial engagement with no public announcement. There was to be a royal tour of South Africa early in 1947 and the King did not want public attention diverted from the tour by any announcement. Princess Elizabeth accepted that it was her duty to forget her personal wishes until after the tour had been completed. George VI later wrote to her: ‘I was rather afraid you had thought I was being very hardhearted about it.’

In his thank-you letter to Queen Elizabeth dated 14 September 1946, Prince Philip wrote: ‘I am sure I do not deserve all the good things which have happened to me. To have been spared in the war and seen victory. To have fallen in love completely and unreservedly makes all one’s personal and even the world’s troubles seem small and petty. I only realise now what a difference those few weeks, which seem to flash past, have made to me. The generous hospitality and warm friendliness did much to restore my faith in permanent values and brighten up a rather warped view of life. Naturally there is one circumstance which has done more for me than anything else in my life.’

Two days before the royal tour of South Africa was due to depart, Dickie Mountbatten gave a small dinner party at Chester Street. The King and Queen were present, though Princess Margaret was absent with a chill. The guests toasted Philip and Elizabeth with champagne, except for the King, who always drank whisky. John Dean says that the royal engagement was in the air that night. The royal family set sail on 1 February 1947 in a new battleship, HMS Vanguard, on a tour that was to last until the middle of May.